The present invention generally relates to apparatuses for detecting positions of reproducing transducers in rotary recording medium reproducing apparatuses, and more particularly to an apparatus for performing detection to detect that a reproducing transducer has reached an outermost peripheral position (lead-in position) and an innermost peripheral position (lead-out position) of a recorded region in a rotary recording medium.
Conventionally, apparatuses for reproducing rotary recording mediums of a so-called electrostatic capacitance type have been reduced into practical use. In this reproducing apparatus, a reproducing stylus makes contact with and slides along a recorded track of the rotary recording medium (hereinafer simply referred to as a disc) in which an information signal such as a video signal is recorded as a variation in geometrical configuration, to reproduce the recorded signal as variations in electrostatic capacitance between the disc and an electrode of the reproducing stylus. In this type of a rotary recording medium reproducing apparatus, a reproducing transducer including the reproducing stylus is transferred along a radial direction of the disc.
On the other hand, the disc is provided with groove guards having a thickness which is thicker than the thickness of the part of the recorded region, at the outermost peripheral edge part and the innermost peripheral part of the disc. Accordingly, when the reproducing transducer is transferred from a resting position to reach the outermost peripheral position (hereinafter referred to as a lead-in position) of the recorded region on the disc upon starting of the reproduction, the reproducing stylus must be in a receded state within the reproducing transducer so that the reproducing stylus does not hit against the groove guard part formed at the outer peripheral edge part of the disc. Furthermore, the reproducing stylus must be lowered to make contact with the disc, when the reproducing transducer reaches the lead-in position of the disc. Moreover, the reproducing stylus must be raised upon completion of the reproduction, when the reproducing stylus reaches the innermost peripheral position (hereinafter referred to as a lead-out position) of the recorded region on the disc.
In addition, it is necessary to perform detection to detect that the reproducing transducer is at a position corresponding to the lead-in position and the lead-out position of the disc, in order to control the transferring speed and the transferring direction of the reproducing transducer and the like, to perform such operations in which the reproducing transducer is transferred from the resting position to the lead-in position at a high speed upon starting of the reproducing, the reproducing transducer is transferred from the lead-in position at a normal reproducing speed, or the transferring direction of the reproducing transducer is reversed at the lead-out position to return the reproducing transducer to the resting position at a high speed, not only to perform operations to lower and raise the above reproducing stylus.
Therefore, conventionally, two switches which are normally open were respectively provided at positions corresponding to the lead-in and lead-out positions of a disc placed onto a turntable, where a projection provided on the reproducing transducer makes contact with and closes the switch when the reproducing transducer reaches the lead-in or lead-out position of the disc. In this conventional apparatus, the construction of the apparatus became complex, and the cost of the apparatus became high, since two switches were required. Further, in the above conventional apparatus, there was a disadvantage in that the transferring direction of the reproducing transducer cannot be detected, although detection can be performed to detect that the reproducing transducer has reached the lead-in or lead-out position of the disc.
The above described switches of the conventional apparatus are constructed to introduce a position detection signal when the switch is closed for a short period of time. Accordingly, in a case where the switch provided at a position corresponding to the lead-out position of the disc breaks down and cannot be put into a closed state, for example, the reproducing stylus is not raised and continues to make contact with the disc, and further, the transferring direction of the reproducing transducer is not reversed. Hence, the reproducing stylus in this state is further transferred towards the inner peripheral direction of the disc, making contact with the disc, and hits against the groove guard at the inner peripheral side. Thus, the reproducing stylus can be damaged to an extent where the reproducing stylus cannot be used again.